I've always wanted something similar to git blame for this. Where I can add notes to sets of lines and toggle whether I want the IDE to display them. Sort of like writing on those overhead projector sheets and saving it to a nearby .notes file or whatever. It'd probably be hell to maintain but a dev can dream.

Tangential, but it sucks that it's hard to even find discussion on something like this. Closest I've found is the fictional "an editor" talk here https://www.destroyallsoftware.com/talks/a-whole-new-world